The invention relates to the design of a fuel nozzle used in a turbine engine.
In a typical turbine engine, a combustor receives compressed air from a compressor section of the turbine engine. Fuel is mixed with the compressed air in the combustor and the fuel-air mixture is then ignited to produce hot combustion gases. The hot combustion gases are routed to the turbine stage of the engine. Typically, a plurality of fuel nozzles are used to deliver fuel into the flow of compressed air within the combustor.
A traditional fuel nozzle is cylindrical in shape, with a cylindrical exterior wall. A plurality of radially extending fuel injectors are attached around a circumference of the exterior wall of the fuel nozzle. At least one fuel delivery port is formed on each of the fuel injectors.
A fuel delivery line is attached to an upstream end of the fuel nozzle. The fuel is typically delivered into an annular shaped primary fuel passageway formed on an inside of the fuel nozzle. The primary fuel passageway delivers fuel to the fuel injectors, and the fuel is ejected out of the fuel delivery ports of the fuel injectors so that it can mix with the compressed air running down the length of the fuel nozzle.
The fuel-air mixture created by the fuel nozzle is then ignited downstream from the fuel nozzle at a location within the combustor. The hot combustion gasses are then routed out of the combustor and into the turbine section of the engine.
Within the combustor, small oscillations in the fuel-air mixture lead to flame oscillations. The flame oscillations in turn generate pressure waves inside the combustor. The pressure waves can travel back to the fuel nozzle to cause a further oscillation in the delivery of additional fuel into the combustor. The interaction between the original oscillations and the further oscillations in the delivery of more fuel can be constructive or destructive. When the interaction is constructive, the oscillations can reinforce one another, resulting in large pressure oscillations within the combustor.
The pressure waves/oscillations, generally referred to as “combustion dynamics,” can be strong enough to physically damage elements located within the combustor. Certainly, they increase the mechanical load on the walls of the combustor. They can also cause incomplete or inefficient combustion of the air-fuel mixture, which can increase undesirable NOx emissions. Further, the oscillations can cause flame flashback and/or flame blowout.